The present invention relates to a data communication apparatus, and more particularly to a data communication apparatus such as a facsimile apparatus in which, if an interrupt request has been made by a call-waiting telephone, whether or not an interruption communication is to be effected is determined depending on whether a distant station is a calling station or a called station.
A call-waiting telephone service is provided by NTT (Nippon Telegraph & Telephone Co., Ltd.). This service allows an interrupt call by another distant station B while a call is being made between one's own station and a distant station A.
Specifically, in a case where the own station is making a call with the distant station A, if the distant station B dials the number of the own station, a predetermined call-waiting signal (interrupt request signal) is sent by an exchange to the own station. Then, if the own station operates a hook button in response to the call-waiting signal, a connection is established between the own station and the distant station B, and a predetermined call-waiting-service holding signal is transmitted from the exchange to the distant station A.
Then, after completion of the call with the distant station B, if the own station operates the hook button again, the own station is connected again to the distant station A.
In the following description, the two stations presently communicating with each other (the distant station A and the own station) will be each referred to simply as the transmitting station or receiving station, and the distant station B attempting an interrupt communication as the interrupting station.
The following are specifications of an example of a call signal and a holding signal of the call-waiting telephone service.
Frequency: 400.+-.10 [Hz] PA0 Output level: -16 [dBm] or less PA0 Tone-on time: 70.+-.10 [ms] PA0 Tone-off time: 70.+-.10 [ms] PA0 Period: 4 [sec] or 8 [sec] (however, generally 4 [sec])
The signal waveform of this example is shown in FIG. 10.
If the call-waiting telephone service is to be received in a case where communication of image information is to be effected by connecting a facsimile apparatus to a telephone line, it suffices if the facsimile apparatus is provided with a means for detecting the call signal of the call-waiting telephone service, and the line is switched over in correspondence with the detection of the call signal.
Such a facsimile apparatus is disclosed in, for instance, Japanese Patent Application Laid-Open No. 62-216584, wherein if the call signal of the call-waiting telephone service is detected by the receiving station (or transmitting station), the line is connected to the interruption station at that point of time. Although a holding signal is outputted from an exchange to the transmitting station (or receiving station) which was in communication up until then, since a general facsimile apparatus is not provided with the capability of detecting the holding signal, the transmitting station (or receiving station) is placed in a state of no signal, so that the line is disconnected after the lapse of a predetermined time. Accordingly, the arrangement provided in the aforementioned publication is such that upon completion of communication with the interrupting station, the receiving station (or transmitting station) automatically dials the number of the transmitting station (or receiving station) which was the station at the other end of the line.
In contrast, Japanese Patent Application Laid-Open No. 64-86660 discloses a technique in which the receiving station (or transmitting station) which effected communication with the interrupting station effects a resetting operation with respect to the distant station with which it had been communicating up until then, before the lapse of a predetermined time from the time when the interrupt communication was started. By virtue of this resetting operation, the distant station does not disconnect the line during the interrupt communication.
In the technique disclosed in the aforementioned Japanese Patent Application Laid-Open No. 64-86660, since the distant station does not disconnect the line, it is substantially possible to set the distant station in a communication-held state.
With this technique, however, since the arrangement provided is such that the station which was called by a call-waiting signal allows the interrupt communication regardless of whether the distant station is a calling station or a called station, if the station concerned is a called station, for instance, the calling station which is the presently communicating distant station is forced to hold the communication.
Since the calling station side pays the fee of the communication line in generally, it is irrational to force the instruction for holding the line to the calling station.